1. Field of the Invention
The present invention relates to a visual field support device and a visual field support method, and particularly relates to technology of generating bird's-eye views from images taken by a plurality of cameras installed at a vehicle and then synthesizing the bird's-eye views. The present invention also relates to an image processor for use in the visual field support device.
2. Description of Related Art
A driver of an automobile or the like, upon running backward, faces difficulty in checking rearview due to the presence of a blind spot. Thus, a system has been already developed which is equipped with an in-car camera for monitoring the rear of a vehicle that is likely to be a blind spot for the driver and which displays a photographed image of the rear on a screen for car navigation or the like.
Moreover, studies have been conducted for, instead of simply displaying a picture with a camera, presenting a more human-friendly picture by use of image processing technology. One of such studies is performing coordinate conversion of a photographed image to thereby generate and display such a bird's-eye view image as is viewed from above the ground. Displaying this bird's-eye view image makes it easier for the driver to recognize condition of the rear of the vehicle.
Furthermore, a visual field support device has been developed which converts images obtained from a plurality of cameras into an all-around bird's-eye view image through geometric conversion and then displays this image on a display section. This visual field support device has an advantage of capable of presenting the driver with condition of all the periphery of the vehicle as a picture viewed from the above, thus covering the surrounding of the vehicle through 360 degrees without any blind spots.
Now, the visual field support device of this type will be described as a conventional example. FIG. 16 is a plan view from above the vehicle 100, showing installation condition of cameras at the vehicle 100. FIG. 17 is a view from the diagonally left front of the vehicle 100. FIG. 17 schematically shows visual fields (photographing regions) of the respective cameras. The vehicle 100 is a truck composed of a driver's cabin and a luggage compartment having a height larger than that of the driver's cabin.
As shown in FIG. 16, the vehicle 100 has cameras (photographing apparatuses) 1F, 1B, 1L, and 1R respectively fitted at the front, rear, left, and right thereof. The cameras 1F, 1B, 1L, and 1R correspond to a front camera, a rear camera, a left side camera, and a right side camera, respectively.
The visual field support device generates bird's-eye view images from images taken by the respective cameras and then synthesizes these bird's-eye view images to thereby display on a display device an all-around bird's-eye view image as shown in FIG. 18. On the display screen of the display device, the vehicle is displayed at the center and the bird's-eye view images respectively obtained from the cameras 1F, 1B, 1L, and 1R are displayed at the front, rear, left and right, respectively, of this vehicle.
There is a portion where visual fields (photographing regions) of the different cameras overlap each other, as shown in FIG. 17. For example, at a given region located diagonally left front of the vehicle 100, the visual fields of the cameras 1F and 1L overlap each other. This overlapping portion corresponds to a region numbered with numeral 101 of FIG. 18. Typically displayed on the region 101 is a picture based on the image photographed by the camera 1F or the image photographed by the camera 1L, or a picture obtained by averaging these images.
The visual field support device of this type performs synthesis processing so that an image has continuity on the ground surface, and thus displays parking slot lines, signs, letters, and the like drawn on the ground surface without any problems. This also applies to the region 101 of FIG. 18. However, a solid object placed on the ground surface is viewed differently at different viewpoints of the camera, thus making it difficult, in principle, to accurately and continuously draw this object in an all-round bird's-eye view image.
For example, consider a case where a person as a solid object 102 is present in a portion (space) where the visual field of the camera 1F and the visual field of the camera 1L overlap each other, as shown in FIG. 19. In this case, when a bird's-eye view image is generated from an image photographed by the camera 1F, the solid object 102 on this bird's-eye view image appears as an image tilted leftward, as shown in FIG. 20. On the other hand, when a bird's-eye view image is generated from an image photographed by the camera 1L, the solid object 102 on this bird's-eye view image appears as an image tilted forward, as shown in FIG. 21.
To synthesize the bird's-eye view image obtained from the camera 1F and the bird's-eye view image obtained from the camera 1L, defining a synthesis boundary 103 as shown in FIGS. 20 and 21 and then simply attaching together the both bird's-eye view images at the synthesis boundary 103 causes a problem that the solid object 102 disappears in an all-round bird's-eye view image obtained through this synthesis.
A possible technique for solving such a problem is generating an image of a common region, where the bird's-eye view image obtained from the camera 1F and the bird's-eye view image obtained from the camera 1L overlap each other, by way of averaging the both bird's-eye view images. However, adopting such an averaging technique results in a solid object appearing as a double image in the all-round bird's-eye view image. Moreover, each image included in the double image is averaged with a background image, which makes it very hard to see the solid object depending on the colors of the solid object and the background.
A method as provided below is a conventional method for separately generating an all-round bird's-eye view image adopting only a bird's-eye view image obtained from the cameral 1F as an image of a common region and an all-round bird's-eye view image adopting only a bird's-eye view image obtained from the cameral 1L as an image of a common region and then displaying these two types of all-around bird's-eye view images on the right and left. A display image in this case appears as a display image 200 of FIG. 22. With this method, however, a plurality of images to be checked by the driver are displayed simultaneously, thus adversely causing confusion, which possibly compromises the security.
There is also a possible method for switching, through, manual or machine operation between adopting an image of a bird's-eye view obtained from the camera 1F as an image of a common region and adopting an image of a bird's-eye view obtained from the camera 1L as an image of a common region. In this case, a display image 201 and a display image 202 shown in FIG. 23 are switched for display. However, switching by the manual operation is complicated, and a picture generated only based on the machine operation is not necessarily a picture in which a solid object can be easily recognized. Further, the switching based on manual or machine operation is equivalent to moving the synthesis boundary to the end of the common region, thus leaving possibility that a display of the solid object around the boundary disappears. That is, it is difficult to avoid, by simple switching, the problem that the solid object disappears.